In: Physics
Why might a heat pump have an advantage over a space heater that converts electrical energy directly into thermal energy?
Heat pumps work on a completely different principle to an
element heater.
Heat pumps simply concentrate a low level thermal source - that is
none of the energy demanded by the heat-pump system is actually
used to raise the temperature directly.
So a large heat reservoir (such as the ground near your house; for
all intents, an inexhaustible reservoir) can be concentrated by the
heat-pump to a much smaller, but warmer 'hot' reservoir (ie. The
space in your house).
For another example a fridge is a heat pump but the 'product' is a
cooler than ambient inside to the fridge rather than a warmer than
ambient interior of a house, etc. As such, home heat pumps can be
reversed to cool in summer.
Peppercorn is (at least this time) quite correct.
Heat pumps take advantage of an energy source (electricity) that
can easily do "work" on a gas by driving a pump to compress it so
that it gives up a lot of heat as it becomes a liquid. The liquid
can then absorb a large amount of heat from its surroundings as it
expands back into a gas.
This method only works if you have an energy source that is capable
of doing work, otherwise you would be able to concentrate heat to
do work without doing any work
An electric heating element is one of the few things wihich is
effectively 100% efficient - that is, it converts all the incoming
electrical energy into heat.
A heat pump can literally pump (move and
'concentrate') heat energy from a nearby reservior (be it
air or ground) ... and might pump perhaps four times as much
heat-energy as it used electrical energy to do the pumping (which
you also get back as heat too). You might therefore get '500%'
efficiency or somesuch in terms of useful heat out compared to
electrical energy in. Exactly how much more energy it pumps depends
on the technology and the temperature difference - the bigger the
temperature difference the harder the pump has to work and the less
efficient it becomes. As you pump the heat out of the reservior,
the reservior becomes colder - if you have a ground-source pump
with too small pipework you might freeze the garden.
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